Electrical Output power in Train for Light and Fan (Rosenberg Generator)

• The most important requirement of train lighting is to obtain constant output irrespective of locomotive speed.
• To achieve this there are three methods of obtaining constant output. They are as follows :

1. Belt Driven Generator
2. Three Brush Generator
3. Rosenberg Generator

1. Belt Driven Generator
2. Three Brush Generator3. Rosenberg Generator :

• The Rosenberg generator is normally used for train lighting.
• This generator is very much similar in construction as that of Metadyne generator.
• It also consists of four brushes located as shown in the Figure
  
• The Rosenberg generator normally does not have the compensation winding.
• Due to this, the entire of the armature reaction opposes the initial excitation.
• The magnetic parts of the machines are not laminated, which help in creating the delay between the excitation and the fluxes.
• This machine is normally used where the rapid response is not required.
• Followings are some of the important properties of Rosenberg generator
• > It produces an EMF in one fixed direction irrespective of direction of rotation.
• > It produces a current which remains constant beyond certain speed.
• The battery of V volts is to be connected with the generator, so as to operate the generator properly.
• Battery supplies the current to the lamps when the train is at rest position.
• Battery also provides supply to the shunt field winding (F).
• The axis of commutation of the brushes MM is in the line with the poles.
• The brushes MM are connected to the battery terminals through rectifier.
• The function of the rectifier to allow the flow of current from battery to the armature only in one direction.
• In addition to the pair of main brushed there are other set of brushes (NN). They are placed at right angles to that of the main brushes (MM).
• When the armature rotates through the magnetic field set up by field FF, current flows through the short circuited armature through NN axis which creates cross field MN.
• The magnetic lines of forces find a low reluctance path through the pole shoes.
• The clockwise rotation results in cross field to set up from left to right. Due to this, the motion of armature through this field generates an EMF and the current along the vertical axis (MM axis).
• The armature MMF (by the arrow MM) opposes the excitation due to the field of field windings FF.
• In the reverse direction i.e. in anti-clockwise direction, the direction of the cross field also reverses.
• The effect of this double reversal prevents the original polarity of the brushes MM.
• The Rosenberg generator may be driven by a belt pullet arrangement by the train axle or mounting the armature directly on the shaft of the axle.
• Figure shows the output current-speed characteristics of Rosenberg generator.
• In this, the no-load component of the armature current will flow until some speed is achieved.

• After this, the further increase in speed will cause the flux to be cut at greater speed, but at the same time, armature current reduces the flux cut by the armature and thereby the output terminal voltage.
• By proper design it can be achieved after certain speed is attained.
• The Rosenberg generator is designed to give the required output current – speed characteristics.